B737 Classic Four Fuel Pumps Uncovered At Takeoff

[LEM]

I have seen on different occasions the four fuel pumps illuminating steady with master caution ON during full thrust takeoffs.

Pitch was never greater than 20 degrees.

Weight was light, airplane climbing like a rocket, forced to retract flaps before acc. height and so on.

I say again, pitch was NORMAL.

Have you had the same in your experience?

Hey you, Mr. Boeing, what the hell do you have to say about that????

:mad:

[Looker]

Try putting a tad more fuel on before departure.

Try moving the thrust levers.

[super 27]

how can you take off with a situation like that:confused: ? have you ever check your boost pumps if they were operative ?

[LEM]

Fuel was 6000kg in all occasions, it's quite common to see the FORWARD pumps illuminating in similar circumstances, but the AFT pumps are not supposed to uncover!

super 27, the pumps were operative, lights extinguished reducing the pitch.
Btw, they are not supposed to illuminate at 17 degrees pitch!!!

It's quite rare to use full thrust at light weights, and it's not everyday that you see 4 pumps illuminated steady!

Maintenance guys didn't even know what to reply to me... :uhoh:

[Intruder]

Different airplane, but similar system: The 747 Classic has restrictions in the DDPG regarding minimum fuel quantities allowed for dispatch with an inop fuel pump. These are predicated on uncovering the forward pump inlet and/or suction bypass at 8 degrees body angle and the aft pump at 18 degrees.

So, it it quite possible that at the fuel quantity you cite, the pump inlets are being uncovered at 17-20 deg body angle and rapid acceleration, and the warnings are valid. Check your 737 pubs for similar restrictions.

[relax.jet]

At 6000kg, at 20deg, even if using full takeoff thrust. I think, the aft pumps should be covered all the time.

[LEM]

Thanks Intruder, the 737 classic DDPG make no reference to pitch attitude but only to fuel qty: at start of takeoff the minimum qty in each main tank (which can hold 4555kg) is 3402kg for an inop aft pump, and 2177kg for a forward pump.

In other words, they tell you the AFT pumps will not uncover with more than 2177kg, not to consider the safety margin they must certainly have included in this figure.

That's why it's amazing that with 3000kg in each main tank you see ALL PUMPS UNCOVERED!!!!

Routinely, with reduced thrust, you never see that, with exactly the same conditions, but at full thrust....

So I will ask again Mr. Boeing, in a very candid way:
IS THAT NORMAL?

[CaptainSandL]

I await Mr Boeings answer to your question on this forum with interest. ;)

Until then… in my experience it is not normal for the aft pumps to become uncovered at anything other than low fuel ops or cavitation. By coincidence I heard recently of a low speed RTO due to m/c FUEL caused by multiple fuel pump LP lights illuminating at start of T/O roll. FoB was 8,000kg (NG).

[LEM]

Thanks Chris, that's what I wanted to hear: NOT NORMAL.
And it's good to have the report of a pilot with your experience.

The story of the NG RTO is even more incredible.

It would be great to have their analysis on what happened.

Btw, I would be prone to think that what I saw might happen at start of takeoff, due to the rapid acceleration, and not after gear retraction.
Although the pitch increases after liftoff, the acceleration is virtually nil, as you (try to) maintain the appropriate speed.

In conclusion, Mr.Boeing, I hope I'll be able to keep a positive souvenir of you before jumping on the scarebus :hmm:

[forget]

One Saturday night in the 70’s a Bangladesh Biman 707 took off (momentarily) at Paya Lebar. I was in Dacca expecting a colleague to arrive on the flight. I called the Biman office to enquire on ETA. All I got was ----- ‘The passengers are alive and well’....click.:eek:

The crew had taken off with minimum fuel on board planning to re-fuel just up the road in Kualu Lumpur. On rotate the very light aircraft immediately went to a massive rate of climb, uncovered all fuel pumps and -------- deafening silence.

My colleague, also a neighbour and aircraft engineer, told a hilarious story of the next 40 minutes – which is how long it took the crash trucks to find a dead 707 lying on the grass! When the engines quit the aircraft was nosed over, gear was up by this time, and down they came. The only indication of terra firma was the grating sounds as the belly contacted the runway. Down the runway they slid and off onto the grass to the right.

The tower then cleared a Qantas 747 for take-off into the crystal clear night -----“Er..... tower, Qantas 01 here. Where’s the Biman ahead of us. We don’t see him’. Another Qantas 74, taxiing on the apron, chipped in. ‘He took-off and came down again. We think he’s still within the airfield.’ Someone in the tower heard this - hit the crash switch and sent the fire trucks to the second 747 where it took ten minutes to convince them they didn’t have a problem. I met the captain of this one in a Hong Kong bar some time later and ‘communications’ with the fire trucks was through the FE opening a door and, eventually, waving them away.

Meanwhile, back on the grass, neighbour had unbuckled himself in a totally silent and dark 707 – walked to the flight deck door and opened it. Empty - with both DV windows open. The flight crew had legged it! Five minutes later and he’s got everyone out of the aircraft and onto the grass, carrying the only casualty - a little old Bengali lady who’d twisted an ankle exiting the aircraft.

Twenty minutes later and still no one had turned up; so neighbour does his Moses trick, noticing that (at least) take-offs were seemingly suspended, and shepherds the passengers across the runway towards the terminal. He made it all the way across followed by 60+ Bengalis of various shapes and sizes, all with lots of cabin baggage, through an open emergency door, up two flights of stairs and into a coffee shop before someone with a uniform said, ‘Er............:confused:

So, uncovered fuel pumps on take-off. It can happen.

[chksix]

Sweet story :ok:

[Lemper]

NIgeria, early eighties, -200, JT8D-15.
LOS-KAD-KAN-SKO-KAN-KAD-LOS.
On four out of those six sectors, all the pumps would uncover; sorry, let me rephrase it: All fuel pump lo press lts would illuminate; pumps uncovered or not, we were not in the tanks to see, however, engines kept on turning and pushing, but the nuisance got us fed up; so on the short sectors we expected the lights to come on, we took off with flaps 25 and accelerated Mack style i.o Ferrari style. No more nuisance.
Of course, we did not have to clear the WTC at the end of a RWY with 20 deg pitch there.

[h73kr]

I await Mr Boeings answer to your question on this forum with interest. ;)

Until then… in my experience it is not normal for the aft pumps to become uncovered at anything other than low fuel ops or cavitation. By coincidence I heard recently of a low speed RTO due to m/c FUEL caused by multiple fuel pump LP lights illuminating at start of T/O roll. FoB was 8,000kg (NG).

...but, on the NG this is a known (and being addressed) issue of the fuel pumps sharing their earthing through one point. Bad earth with vibration at take-off power resulting in pump lights flickering. Doubt it's the same issue here.

[Denti]

Never had 4 low pressure lights on, 2 (forward) are very common. Just my 0.02$ of experience for the last 7 years on the classic with normal fuel loads between 4.800kg and 6000kg of fuel.